Large carceplexes

Large Carceplexes from Cyclic Arrays of Cavitands... 

A large carcerand has a cavity volume of 120 A3. If the molecular volume of methane is 28.5 A3, calculate the occupancy factor, p, for a 1 1 methane carceplex of this host. What host volume would result in an occupancy factor of 0.67, equivalent to solid methane Calculate the notional pressure of one molecule of methane in a cavity of this size. Do you think that such a carceplex is likely to form ... 

Fig.6 The mechanism by which the Cs+S avitand ion pair on the lower hemisphere reacts with the CH2C1 group of the upper hemisphere in an SN2 manner during the cage closure leads to a large amount of Cs+ being present within the carceplex in the final samples...

Table 4-1 shows that pyrazine is the best template and is a million times better than the poorest measurable template, iV-methyl-2-pyrrolidinone (NMP) [14]. Also, considering the series of suitable guest molecules, the selectivity is unusually high, where small perturbations in guest structure can lead to large differences in templating abilities [14]. For example, methyl acetate is 10000 times better than ethyl acetate [14]. A similar template effect has also been observed in the formation of carceplex Ic guest [15]. 

A cap molecule of suitable size and symmetry could effectively close off the interior of trimer 7 to create a very large molecular container. Such a feat has recently been accomplished in our laboratories, where trimer carceplex 9 -3 DMF was synthesized in 37% yield, by reaction of trimer 7 with 2,4,6-tris(bromomethyl)mesitylene under basic conditions (Scheme 4-4) [21]. No empty trimer carcerand has yet been isolated, which implies that a template (or templates) is required for formation. Can a large single template molecule form trimer carceplex 9-guest We are currently investigating this possibility. Such an investigation begs the question when does a template effect become a solvent effect ... 

Closely related to carceplexes are hemicarceplexes, for which some template studies have been undertaken. A wide range of hemicarceplexes have been synthesized to date, most of which involve the linkage of two cavitands, where a wide variety of differently sized spacers have been incorporated. Thus, fairly large-ring portals have been created in the hemicarceplex skin, which allow entrapped guest molecules to escape into the external medium. 

A potential for large ring and cavity formation extends to many P-containing organic molecules, in addition to the inorganic phosphates discussed above. These compounds include phosphate derivatives of fashionable structures such as crown ethers, calixarenes, carceplexes, catenanes, rotaxanes, self-assembly molecules and so on, and varieties which are discussed in Chapter 10, such as cyclo-dextrins, phosphosaccharides, phosphoproteins and nucleic acids. Phosphorus analogues of cyclo-polypyridyls and porphyrins are discussed in Chapters 7 and 8. 

Since the first carceplex synthesis, a large variety of hemicarcerands have been prepared by connecting two cavitands with four appropriate linkers, and their binding properties have been studied (Figure These hemicarcerands... 

The effect of solvent in this process is substantial, and very large solvent effects on the rate of the first step (hemi-carceplex dissociation) are observed. In combination with the large unfavorable entropic contributions to constrictive... 

As well as serving as useful hosts and precursors to extended carceplexes [234]. Gibb showed in 2003 that cavitands such as 72 can be cleaved to form large macrocycles (e.g., 73 Scheme 9.7) [235]. 

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